Alpine touring bindings allow the heel of the user's footwear (such as a ski boot) to be latched to a snow travel aid (such as a ski), for sliding downhill (the “downhill mode”) and allow the heel to be released for walking and climbing (the “touring mode”). Release bindings allow the footwear to release from the snow travel aid when in the downhill mode, in case of a fall. When in the touring mode, the user may climb or walk with a great degree of freedom since the footwear is pivotally engaged with the aid near the toe of the footwear while the heel of the footwear is free to move upward and downward relative to the aid. A historical collection of such bindings can be viewed in the “Virtual Museum of Backcountry Skiing Bindings” at www.wildsnow.com, authored by Louis Dawson.
Alpine touring bindings sold under the brand DYNAFIT are release bindings that take advantage of the fact that modern alpine touring boots have a rigid sole. Thus, it is unnecessary to provide a bar, plate or other arrangement connecting the toe and heel units, as is the case with many other alpine touring bindings (see patent publications EP0199098, EP0519243, EP1559457, and AT402020). Unlike other release bindings, lateral release of the DYNAFIT™ system is provided at the heel, not the toe.
The DYNAFIT™ binding system comprises a toe unit which has a set of laterally oriented jaws. Such jaws open and close in a direction generally perpendicular to the longitudinal axis of a ski or other snow travel aid so as to grasp opposite sides of the toe region of the user's footwear. The axes of rotation of each jaw in the DYNAFIT™ system is oriented generally parallel to the longitudinal axes of the snow travel aid. The toe unit is mounted at an appropriate location on the upper surface of the snow travel aid. A separate heel unit is mounted at a particular region on the upper surface of the snow travel aid rearward of the toe unit, the location of which is dictated by the length of the footwear sole. The heel unit typically comprises two pins which extend forward to engage opposite sides of a fitting placed over a cavity in the rear of the footwear heel. Under forward release conditions, the pins are forced apart against spring pressure to disengage from the fitting.
Lateral release in the DYNAFIT™ system is provided by the heel unit being rotatable on a generally vertical post. Adjustment of the lateral release is done by altering resistance to rotation of the heel unit. While the jaws of the toe unit open, they do so with a relatively high resistance to force in order to provide a constrained fulcrum that acts as the pivot point for the lateral release feature of the binding system. Thus, the toe unit of a DYNAFIT™ system is not considered a lateral release toe unit such as is employed in other binding systems. An example of a binding system in which the toe unit is a lateral release toe unit containing jaws for grasping the toe is described in WO2007/010392. The latter binding system operates differently from the DYNAFIT™ system because the toe unit rather than the heel unit provides lateral release.
To switch between touring and downhill modes with the DYNAFIT™ system, it is necessary to rotate the heel unit so that the pins either engage the footwear heel (downhill mode) or face away from the heel (touring mode). When the pins are facing away, the heel is free to move upward and downward with the toe of the footwear being pivotally engaged to the toe unit. In order to switch from downhill mode to touring mode it is necessary to either forcibly release the pins from the fitting on the heel (not recommended) or disengage the jaws of the toe unit from the footwear toe, so that the footwear completely exits from the binding system whereupon the heel unit may be rotated to a position in the touring mode. Subsequent re-entry of the toe into the toe unit is then required. This process is time consuming and can be difficult to do in deep snow or on a steep slope, for the reasons discussed below.
The jaws of a DYNAFIT™ binding system toe unit open by spreading outwards away from the longitudinal midline of a snow travel aid. Each jaw has an arm that extends towards the midline. Each arm has an end that abuts the other in an end-to-end manner. In the commercial embodiment, one such end engages a recess in the other end. In each of the open and closed positions, the jaw arms ends are in an over-centre position and springs bias the jaws towards either the fully opened or the fully closed positions. Each jaw has a generally conical “tooth” which laterally engages a corresponding fitting embedded on the side of the toe region of the footwear sole. When the jaws are closed and engage these fittings, the toe is retained adjacent the upper surface of the snow travel aid but the footwear is able to pivot in a forward or backward direction to facilitate walking and climbing. A catch is provided to prevent the jaws from inadvertently opening as a result of application of force sufficient to overcome the spring pressure, and is used when the toe unit is in the touring mode. The catch is usually disengaged in the downhill mode so as to not prevent release of the footwear during a fall. The user enters the toe unit by carefully positioning the footwear toe between the jaws so that the teeth will engage the toe fittings when the toe is depressed, causing the jaws to close. This manoeuvre requires patience and practice.
Since the jaws in the DYNAFIT™ system toe unit make use of an “over-centre” arrangement to retain the jaws in either the open or closed position, the distance between the tooth of each jaw and the footwear toe is substantial when the jaws are in the fully opened position. This makes it difficult for the user to confidently align the toe between the jaws, particularly if the toe and/or binding is visually obscured by snow or the snow travel aid is resting on an inclined snow surface.
EP1559457 discloses an improvement in the DYNAFIT™ system boot toe fitting which is intended to assist the user in entering the toe unit. This improvement involves the presence of flanges on the toe fittings, which define a vertical groove in the fitting. The flanges come closer to the teeth of the binding jaws when the binding is in the open position than is the case with previous fittings and help guide the user to place the toe in the most appropriate position (see FIG. 6 of EP1559457). Nevertheless, practise is still required for the efficient use of the binding and it is not practical to retrofit the improved fittings into footwear containing the previous fittings.